Accumulating evidence suggests that chronic exposure to particulate matter (PM) negatively affects growth of lung function in children and can lead to COPD in adults, but there is a dearth of information on the long-term effects of early life exposure to PM. In the proposed research we address the effects of exposure during infancy to biomass smoke PM on respiratory health later in childhood. Our mechanistic hypothesis is that the combustion-generated organic compounds present on fine particles in biomass smoke induce oxidative stress, upregulation of inflammatory cytokine production, and subsequent airway inflammation. Variation in the genotypes of key antioxidant enzymes (e.g., GSTM1 and GSTP1) may help to identify which children are more susceptible to the effects of inhaled PM on respiratory health. We propose to conduct a longitudinal follow-up study of a birth cohort of infants currently enrolled in a NIH-funded, randomized stove intervention trial to reduce acute lower respiratory illness (ALRI) in rural Guatemala. The improved cookstove markedly reduces biomass smoke exposure. After the participating child is 18 months old all families are offered the improved stove. Our proposed longitudinal follow-up study is designed to a) determine whether exposure to higher levels of PM during the first 18 months of life is associated with increased respiratory symptoms, bronchodilator responsiveness, sensitization to aeroallergens, and decreased rate of growth of lung function and somatic growth; and b) determine whether the GSTM1 null genotype renders children more susceptible and the GSTP1val105 variant less susceptible to the development of PM-induced oxidative stress and chronic respiratory effects. The effects of biomass smoke exposure have never been studied in a longitudinal design with quantitative exposure assessment. The current randomized intervention trial provides a unique opportunity to study the long-term effects of high exposure to biomass smoke/PM during the critical time window of lung development if follow-up is extended until later in childhood.